Monday, January 14, 2008

Sample Lab Report

Below is a sample lab I wrote for the Eggsperiment. You may use this as a guide for writing your papers. Pay close attention to formatting & use of the past tense.

Ms. Saxe

A Block

Month Day, Year

The Effect of Various Concentrations of Sugar Solutions

on the Percent Change in Mass of a Chicken Egg.

INTRODUCTION

Osmosis and diffusion are essential to maintaining equilibrium of solutes and water in cells. Osmosis is the movement of water across a semi-permeable membrane, where as diffusion is the movement of solutes from an area of high concentration to an area of low concentration1. Various transport proteins located in the cell membrane assist in moving large solute molecules across the cell membrane. Solutions where the concentration of solutes outside of the cell is less than in the cell are said to be hypotonic. Cells in hypotonic solutions tend to swell as water enters the cell to maintain equilibrium. Solutions where the concentration of solutes outside the cell is greater than inside the cell are hypertonic. In hypertonic solutions, water leaves the cell to try to maintain equilibrium. Lastly, when the concentration of solutes outside and inside the cell is equal the solution is isotonic. Using a chicken egg (without a shell) as a model of the cell membrane, is it possible to observe the effects of osmosis with the naked eye? If an egg without a shell is placed in a sugar solution, then there will be some change in the mass of the egg due to osmosis.

MATERIALS & METHODS

One dozen large white chicken eggs from the Jackson Star supermarket were submerged in Best’s white vinegar for 72 hours in a three liter bowl. During this period, every 24 hours the vinegar was changed to increase the rate at which the shell decomposed. Eggs were moved around in the vinegar once every 24 hours to ensure all sides of the shells were equally submerged. Any time eggs were handled rubber gloves were used to protect the individual from any bacteria that may have been present. After 72 hours, the eggs were ready to be used for the experiment.

The control egg was removed from the vinegar and weighed on an electronic balance to obtain the initial mass. This egg was placed in a 400mL beaker containing 350mL of tap water and labeled as the control. The experimental egg was weighed using an electronic balance and placed aside in a weigh boat while the sugar solution was created. The sugar solution contained 15g of table sugar and 35g of sucrose added to 250mL of tap water, in a 400mL beaker. The sugar solution was stirred thoroughly until all of the grains of sugar were dissolved. The sugar concentrations were recorded in a data table on a lab handout. The beaker was labeled with the last names of group members, class block and placed in a cabinet to sit undisturbed for 48 hours over the weekend. After 48 hours, the secondary observations of the egg were completed including obtaining the final mass of the egg using an electronic balance. Final mass was recorded in the lab handout. Eggs were disposed of by the instructor.

RESULTS

The overall results in E and F block varied greatly: in E block all of the eggs had a negative percent change meaning that they gained mass, where as in F block, all of the eggs had a positive percent change meaning they lost mass.


Figure 1: This graph shows the percent change in mass for all of the eggs tested. Egg number 1 is the control. Eggs 2-5 were from E block and eggs 6-8 were from F block.

DISCUSSION

Perhaps what is most interesting to note about this experiment is that each block experienced the same overall result: E block eggs were all placed in hypotonic solutions and F block eggs were all placed in hypertonic solutions. The results do support the hypothesis that, if an egg is placed in a sugar solution a change in mass will occur. No possible explanation can be found at this current time to explain why the eggs in the various classes reacted so differently to the solutions. Possible sources of error for this experiment include: incorrect labeling of sugar in the large plastic bag; incorrect notation for what and how much was placed in solution and allow the eggs to sit for too long in solution. The table sugar that was used for this lab came from the chem. storage room and had been sitting for an unknown amount of time in a plastic baggy that was loosely secured with a knot. Exposure to fumes and potentially other chemicals may have left residue in the sugar which changed how it reacted in the experiment. If the solutes added to water were incorrectly written down this could certainly have impacted how the eggs reacted. Lastly, since the eggs sat over the weekend, nobody observed them at 24 hours, perhaps the greatest change in mass was visible then, but nobody was able to observe it. Further study would be needed to determine the possible causes of the anomalies in the results.

CONCLUSION

While the data in this experiment is inconsistent between E and F blocks, it does support the hypothesis that if an egg is placed in a sugar solution there will be a change in mass. Further tests using a larger sample size would be needed to establish more consistent events.

ACKNOWLEDGEMENTS

Thanks to Mr. Brummer for supplying the vinegar and Ms. Saxe for soaking the eggs in advance so they could be used in the experiment.


LITERATURE CITED

1. Memorial University of Newfoundland. Principles of Osmosis and Diffusion. [Online]. October 22, 2007 URL: http://www.mun.ca/biology/Osmosis_Diffusion/tutor2.html

4 comments:

Anonymous said...

thanks for beeing so generous

faizan said...

The whole matter has authenticity in itself which is perfect for students.

Charlotte said...

Would you mind if I used this as a resource for a lesson I am teaching about how to write a lab report? I would, of course, cite your work!

Saxe said...

Sure Charlotte, that's completely fine. I'm glad you found it helpful.